Diamonds are a popular gift for Valentine's Day, but shoppers often pay too much for stones. Chicago Consumers' Checkbook visited ABC 7 on Wednesday with some advice for diamond buyers to avoid overspending.

Nonprofit Chicago Consumers' Checkbook's undercover shoppers found that in the Chicago area, depending on the store, shoppers pay $6,514 to more than $15,000 for essentially the same one-carat diamond and $11,000 to more than $20,000 for a 1.5-carat diamond

While shoppers can waste a lot of money by buying at a high-cost retailer, people also spend too much buying at a store that pushes customers toward "perfect" stones that cost thousands of dollars more than "imperfect" ones-on which no one can detect imperfections without a microscope.

When buying a diamond, follow this advice:

Educate yourself. The best way to protect yourself from a dishonest diamond dealer is to demonstrate you know what you're doing. Our advice on how diamonds are graded and priced and our tips on what you should (and shouldn't) care about is a good start.

Focus on value. Think about whether or not you care about very small or even undistinguishable differences. You'll get a lot more bang for your extra bucks by buying an ideal-cut diamond. But if you can't otherwise discern differences in quality between two stones, don't pay more for the higher-quality stone. Most shoppers should avoid paying extra for diamonds with color grades above F or with clarity scores better than SI1. And avoid stones that weigh in at popular or round-number carat cutoffs.

Stick with GIA-certified stones. If the store can tell you only that a diamond is "certified," without a designation from the GIA or other reputable organization, ask to see something else. Many other certifications tell you nothing about stone quality.

The more options a store can show you, the better. If a store shows you just one stone, that's a red flag. Be wary of retailers that start by asking you to compare very dark stones with very light ones, or to judge well-cut gems against poorly cut ones. These comparisons are often intentionally simplistic and done to push customers into paying too much for clearly superior stones.

Give yourself plenty of time. It takes a few days or weeks for loose stones to ship to the store.

Consider alternatives. Sapphires, rubies, and other stones offer similar dazzle at significantly lower prices. Many diamonds (and lots of other gems) are still mined in areas with deplorable working conditions and violence. And most mines are environmental nightmares. But lab-grown diamonds are chemically and physically identical to mined diamonds but cost about 30 percent less.

Review the return policy. Buy from stores that offer returns with a full refund within 30 days. But if you purchase a custom setting, know you'll likely pay for design and fabrication costs. Have the store put in writing how much of a refund you'll get in that case.

Get it appraised. After purchasing an expensive diamond, take it to an independent appraiser. Although you'll have to pay about $50 to $200 for the appraisal, it's good insurance against being given-either intentionally or by mistake-a switched-out gem that's of lower quality than what you paid for.Pay by credit card. If a store doesn't come through, you'll have the option of disputing the charge with your credit card company.

There are lots of great alternatives to diamonds, such as lab-created stones. They cost much less and are gaining popularity because they are ethically sourced.